THE LARVAL STAGES 89 



exception, above 200 metres. In other words, it belongs to the Antarctic surface layer'. The later 

 work of Fraser (1936) based on the analyses of over 2000 vertical net hauls, the majority of them 

 extending down to depths more than twice those of the ' Vikingen ' series, has shown that of the three 

 Calyptopis stages the First ranges in substantial numbers from the surface down to 750 m. and, 

 therefore, strictly speaking, 'belongs' to both warm deep and surface currents, while the Meta- 

 nauplius, of which Fraser found several thousands, is revealed as spending its entire existence in the 

 warm deep layer.^ Fraser's discovery of the deep habitat of the Metanauplius is of far-reaching 

 importance since as will be shown presently it proves to be the key to much of what has since become 

 known of the life-history and vertical and horizontal movements of the larvae which are now to be 

 described. In the meantime it may be noted that Ruud too records the Metanauplius from the 

 warm deep layer, the few specimens of this stage he determined all having been taken in the deeper 

 of the two net hauls he examined. He regarded their presence at this level, however, as abnormal, 

 believing 'that these very young larvae, like the eggs, should be looked for close up to the drifting 

 ice '. He did not, therefore, suspect them for what they must have been — stragglers from a much 

 larger population living at depths beyond the range of his deepest nets. 



The analysis of over 5000 vertical samples completed since Fraser's work was published not only 

 establishes beyond all doubt the permanent deep habitat of the Metanauplius in oceanic water, but 

 reveals no less certainly the still deeper habitat of the Second Nauplius of which Fraser found only 

 seven specimens and Ruud, in his shallow nets, none at all. The principal results of these later analyses 

 with which I have incorporated the principal results of Fraser's are set out in Tables 13-15, Tables 13 

 and 14 showing the vertical distribution of the oceanic larvae of the Weddell and East Wind zones at 

 stations where deep-living Nauplii and Metanauplii were encountered. Table 15 the corresponding 

 distribution in this dual current system and elsewhere at stations where such early deep-living stages 

 were absent. 



The salient facts emerging from these analyses may be summarised as follows: 



(i) It is when the Metanauplius is encountered, and then only, that the immediate product of its 



moulting, the First Calyptopis, ranges from the Antarctic surface layer well down into the warm 



counter-flowing deep current, it being particularly abundant down to 750 m. and probably reaching 



the extreme downward limit of its bathymetric range somewhere between this deep level and 1000 m. 



(2) The analyses reveal and repeatedly emphasise the deep habitat of the Metanauplius, showing it 

 to be a stage that apart from occasional rare stragglers^ has not been recorded by us above the 500 m. 

 level. It appears to be most abundant between 1000 and 500 m., the observations we have below this 

 level suggesting that the lowermost limit of its vertical range, as revealed for example at Station 2594* 

 (Table 13) and Station 2603 (Table 14), occurs somewhere between 1500 and 1000 m. 



(3) They reveal for the first time substantial concentrations of the hitherto rarely seen Second 

 Nauplius and give some indication of its probable position in the bathymetric scale. Although 

 recorded twice in large numbers between 1000 and 750 m. (Table 13, Stations 823 and 2594) it has 

 in fact very rarely been encountered there. For the period November-April in the East Wind- 

 Weddell zone we have 360 stations with net hauls down to 1000 m., the Second Nauplius, apart 

 from an odd straggler or two, being absent from the 1000-750 m. level except at the two stations 



1 That is, in deep oceanic water beyond the Antarctic continental shelf. See, however, p. 205. 



^ These have been disregarded. They always occurred when the catch in the 750-500 m. layer was particularly heavy and, 

 therefore, it is suspected, may have got left over in the net hauled from the deeper level. 



3 The deep (1500-1000 m.) net at this station failed to close and fished open to the surface (see p. 100). It produced, 

 however, a far larger gathering of Nauplii and Metanauplii than the 1000-750 m. net, much of it there is little doubt from 

 the 1 500-1000 m. level. The estimated catch at the deeper level has been obtained by subtracting the 1000-750 m. catch from 

 the large total taken in the 1500-0 m. net. 



